This invention relates to a light-emitting semiconductor device, in which ohmic contacts of two polarities are made substantially on the same surface of a semiconductor chip without using any wire, and a method of fabricating the same.
Conventional light-emitting semiconductor devices generally adopt wire bonding to make an ohmic contact. In a p-n junction device two ohmic electrodes are formed respectively on the front and back sides of the device, so that a fine wire needs to be attached to one of the electrodes to connect it, for example, to a terminal post while the other electrode can be brought into face-to-face contact with a surface of a stem. In a device in which a junction is formed between an n-type layer and a semi-insulating layer, an ohmic contact is made to the side face of the n-type layer by attaching a fine wire thereto.
The employment of wire bonding causes inconvenience to the fabrication of the devices, particularly significantly for devices comprising a number of light-emitting semiconductor chips, and places various restrictions on the design of lenses for the devices and stems or boards on which light-emitting semiconductor chips are mounted. Furthermore, the products often suffer from insufficient reliability.
Recently there is an increasing demand for high reliability light-emitting semiconductor devices which do not employ wire bonding but nevertheless are comparable to conventional devices of the wire bonding type both in cost and performance. The demand would be met by providing light-emitting semiconductor chips of flip-chip structure with solder bumps if industrial fabrication of such chips is easier than the fabrication of silicon devices of the same type. However, development of such chips has encountered various difficulties because, unlike silicon planer devices, light-emitting semiconductor chips generally do not allow the provision of two electrodes on the same plane and are devoid of a protective coating of an insulating material such as SiO.sub.2. Another problem is that gold alloy electrodes of conventional light-emitting semiconductor chips are liable to melt into solder during buidup of solder bumps. In the case of applying a solder bump technique used for silicon devices to light-emitting semiconductor chips, therefore, the electrodes of the chips are required of a multi-layer structure and a photolithographic process needs to be repeated several times.